How to generate a random boolean using JavaScript ?

Last Updated : 12 Sep, 2019

The task is to generate random boolean value. Here we are going to use JavaScript to achieve the goal.

Approach 1:

Calculate Math.random() function.
If it is less than 0.5, then true otherwise false.

Example 1: This example implements the above approach.

<!DOCTYPE HTML>  
<html>  
  
<head>  
    <title>  
        How to generate a random  
        boolean using JavaScript? 
    </title> 
</head>  
  
<body style = "text-align:center;" id = "body">  
      
    <h1 id = "h1" style = "color:green;" >  
        GeeksForGeeks  
    </h1> 
      
    <p id = "GFG_UP" style =  
        "font-size: 15px; font-weight: bold;"> 
    </p> 
      
    <button onclick = "gfg_Run()">  
        Click here 
    </button> 
      
    <p id = "GFG_DOWN" style =  
        "font-size: 23px; font-weight: bold; color: green; "> 
    </p> 
      
    <script> 
        var el_up = document.getElementById("GFG_UP"); 
        var el_down = document.getElementById("GFG_DOWN"); 
          
        el_up.innerHTML = "Click on the button to " 
                        + "generate random boolean."; 
          
        function gfg_Run() { 
            el_down.innerHTML = Math.random() >= 0.5; 
        }          
    </script>  
</body>  
  
</html> 

Output:

Before clicking on the button:
After clicking on the button:

Approach 2:

Create an array containing ‘true’ and ‘false’ values.
Calculate Math.random() and round its value.
Use rounded value as the index to the array, to get boolean.

Example 2: This example implements the above approach.

<!DOCTYPE HTML>   
<html>   
  
<head>  
    <title>  
        How to generate a random 
        boolean using JavaScript? 
    </title> 
</head>  
  
<body style = "text-align:center;" id = "body">   
      
    <h1 id = "h1" style = "color:green;" >   
        GeeksForGeeks   
    </h1> 
      
    <p id = "GFG_UP" style =  
            "font-size: 15px; font-weight: bold;"> 
    </p> 
      
    <button onclick = "gfg_Run()">  
        Click here 
    </button> 
      
    <p id = "GFG_DOWN" style =  
        "font-size: 23px; font-weight: bold; color: green; "> 
    </p> 
      
    <script> 
        var el_up = document.getElementById("GFG_UP"); 
        var el_down = document.getElementById("GFG_DOWN"); 
        var ar = [true, false]; 
          
        el_up.innerHTML = "Click on the button to " 
                        + "generate random boolean."; 
      
        function gfg_Run() { 
            var index = Math.round(Math.random()); 
            el_down.innerHTML = ar[index]; 
        }          
    </script>  
</body>   
  
</html> 